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# Dental researchers recently discovered that tooth-brushes

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Dental researchers recently discovered that tooth-brushes [#permalink]

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18 Jul 2008, 02:18
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Official Guide for GMAT Verbal Review, 2nd Edition

Practice Question
Question No.: 41
Page: 132
Difficulty:

Dental researchers recently discovered that tooth-brushes can become contaminated with bacterial that cause pneumonia and strep throat. They found that contamination usually occurs after toothbrushes have been used for four weeks. For that reason, people should replace their toothbrushes at least once a month.

Which of the following, if true, would most weaken the conclusion above?

(A) The dental researchers could not discover why toothbrush contamination usually occurred only after toothbrushes had been used for four weeks.

(B) The dental researchers failed to investigate contamination of toothbrushes by viruses, yeasts, and other pathogenic microorganisms.

(C) The dental researchers found that among people who used toothbrushes contaminated with bacterial that cause pneumonia and strep throat, the incidence of these diseases was no higher than among people who used uncontaminated toothbrushes.

(D) The dental researchers found that people who rinsed their toothbrushes thoroughly in hot water after each use were as likely to have contaminated toothbrushes as were people who only rinsed their toothbrushes hurriedly in cold water after each use.

(E) The dental researchers found that, after six weeks of use, greater length of use of a toothbrush did not correlate with a higher number of bacterial being present.
[Reveal] Spoiler: OA

Last edited by Narenn on 07 Oct 2013, 10:44, edited 3 times in total.
Necessary Corrections for Official Guide Verbal Review 2nd Edition Project
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18 Jul 2008, 02:35
I think the answer is C. I am not 100% sure.
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18 Jul 2008, 04:53
i am also leaning towards C. The researches are saying to replace the tootbrush once a month in order to avoid being affected by the viruses ... to weaken, we are basically saying that regardless of whether brush is replaced or not, rate of getting the virus is the same
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18 Jul 2008, 06:14
E

vksunder wrote:
Dental researchers recently discovered that tooth-brushes can become contaminated wth bacterial that
cause pneumonia and strep throat. They found that contamination usually occurs after toothbrushes have been
used for four weeks. For that reason, people should replace their toothbrushes at least once a month.
Which of the following, if true, would most weaken the conclusion above?
(A) The dental researchers could not discover why toothbrush contamination usually occurred only after toothbrushes had been used for four weeks.
Not knowing why doesn't attack the basis for the conclusion. It just means it happens, but we don't know why. No reason to think they're wrong.
(B) The dental researchers failed to investigate contamination of toothbrushes by viruses, yeasts, and other pathogenic microorganisms.
Out of scope. It doesn't matter that they failed to investigate other contamination, the focus is on the contamination they DID find.
(C) The dental researchers found that among people who used toothbrushes contaminated with bacterial that cause pneumonia and strep throat, the incidence of these diseases was no higher than among people who used uncontaminated toothbrushes.
This is a close one, but in the end incorrect. The premise of the stem is all about the length of time the person uses the toothbrush. That is not mentioned at all here. It does weaken, but E weakens more because it undercuts the basic reason for the stem's conclusion.
(D) The dental researchers found that people who rinsed their toothbrushes thoroughly in hot water after each use were as likely to have contaminated toothbrushes as were people who only rinsed their toothbrushes hurriedly in cold water after each use.
Out of Scope. This has nothing to do the length of time the toothbrush is used. This has to do with a variable that changes from person to person. The length of use has to do with every toothbrush user. This doesn't weaken the stem.
(E) The dental researchers found that, after six weeks of use, greater length of use of a toothbrush did not correlate with a higher number of bacterial being present.
This undercuts the premise of the stem by saying that after 6 weeks of use, there is no difference between toothbrushes. Sure their correlation worked after 4 weeks, but any variation was completely gone within 2 more weeks and their conclusion that we should toss the toothbrush after 4 weeks is invalid because it doesn't hold true after 6 weeks.

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Re: Dental researchers recently discovered that tooth-brushes [#permalink]

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23 Mar 2012, 10:57
I have chosen the answer C for this question:

The underlying assumption in the passage is that contamination with bacteria can cause illness among individuals. Therefore, we should be switching toothbrushes once a month to avoid this.

A. The fact that dental researchers could not discover why contamination happens does not matter because the contamination still happens and can cause illness. Therefore, individuals should still replace their toothbrushes. This answer choice does not weaken the argument.

B. This is irrelevant - we do not care that dental researchers did not investigate other types of contamination.

C. This is the correct answer. If individuals who use toothbrushes that are contaminated do not get any sicker than individuals who use uncontaminated toothbrushes, then changing the toothbrush every month is unnecessary.

D. This somewhat supports the argument because careful cleaning of the toothbrush does nothing to eliminate the contamination, so people should be continually changing toothbrushes.

E. The fact that the amount of bacteria did not increase does not weaken the argument. The reason is because there is still a certain amount of bacteria on the toothbrush that could cause illness to individuals.
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Re: Dental researchers recently discovered that tooth-brushes [#permalink]

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23 Mar 2012, 12:14
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Conclusion: People should throw away their toothbrushes after only four weeks of use.

Reasoning: In that time, enough bacteria has accumulated to cause strep throat and pneumonia.

To WEAKEN this argument we will need an answer choice that suggests we should not dispose of our 4-week old toothbrushes.

It seems that debate here is between (C) and (E), so I will focus on these two answer choices.

(C) The dental researchers found that among people who used toothbrushes contaminated with bacteria that
cause pneumonia and strep throat, the incidence of these diseases was no higher than among people who
used uncontaminated toothbrushes.

Contaminated toothbrushes, i.e. those brushes with bacteria, are no more likely to cause strep throat than non-contaminated toothbrushes. Therefore, one should not throw away their 4-week old toothbrushes. ANSWER.

(E) The dental researchers found that, after six weeks of use, greater length of use of a toothbrush did not
correlate with a higher number of bacterial being present.

Let's say I have a contaminated 4-week old toothbrush, on which a small colony bacteria has grown. If I do not throw the toothbrush away, I am likely to get strep throat. Nevertheless, I continue using the toothbrush for another two weeks. Now at week 6 the colony of bacteria is still there. According to answer (E) the colony has not grown (greater length of use of a toothbrush did not correlate...)

Of course I should still throw the toothbrush away because it is contaminated. Remember, we have to find an answer choice that suggests that it makes no sense throwing our toothbrush away. (E) however suggests that we should still throw the toothbrush away at week 6, regardless of whether it is less contaminated than it was at week 4.
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Re: Dental researchers recently discovered that tooth-brushes [#permalink]

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31 Oct 2013, 03:00
Bumping for review and further discussion*.

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Re: Dental researchers recently discovered that tooth-brushes [#permalink]

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03 Jul 2014, 06:56
vksunder wrote:
Official Guide for GMAT Verbal Review, 2nd Edition

Practice Question
Question No.: 41
Page: 132
Difficulty:

Dental researchers recently discovered that tooth-brushes can become contaminated with bacterial that cause pneumonia and strep throat. They found that contamination usually occurs after toothbrushes have been used for four weeks. For that reason, people should replace their toothbrushes at least once a month.

Which of the following, if true, would most weaken the conclusion above?

(A) The dental researchers could not discover why toothbrush contamination usually occurred only after toothbrushes had been used for four weeks.

(B) The dental researchers failed to investigate contamination of toothbrushes by viruses, yeasts, and other pathogenic microorganisms.

(C) The dental researchers found that among people who used toothbrushes contaminated with bacterial that cause pneumonia and strep throat, the incidence of these diseases was no higher than among people who used uncontaminated toothbrushes.

(D) The dental researchers found that people who rinsed their toothbrushes thoroughly in hot water after each use were as likely to have contaminated toothbrushes as were people who only rinsed their toothbrushes hurriedly in cold water after each use.

(E) The dental researchers found that, after six weeks of use, greater length of use of a toothbrush did not correlate with a higher number of bacterial being present.

This is a good causal problem

Contaminated brush (X) caused pneumonia and step throat (Y) . One way to weaken the causal issue is

Even if cause does occurs effect occurs (No X ---> still Y)
Ans C says that even uncontaminated brush cased pneumonia and step throat (Y)

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Re: Dental researchers recently discovered that tooth-brushes [#permalink]

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14 Sep 2015, 05:34
Hello from the GMAT Club VerbalBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
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Re: Dental researchers recently discovered that tooth-brushes [#permalink]

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14 Apr 2016, 12:56
Conclusion: people should replace toothbrush at least once a month
Premise: Toothbrush gets contaminated with bacteria after 4 weeks of use.

Assumption: bacterial is more likely to cause illness

answer choice will undermine this assumption

Alternatively: Negate conclusion and select answer choice that supports the negated conclusion along with the premise.
Negated Conclusion: people should not replace toothbrush at least in a month.
Re: Dental researchers recently discovered that tooth-brushes   [#permalink] 14 Apr 2016, 12:56
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